1. Field of Invention
The present invention relates to a process for halogenating aminobenzotrifluorides to produce 2-amino-5-halobenzotrifluoride to the virtual exclusion of other monohalogenated isomers.
2. Prior Art
2-Amino-5-chlorobenzotrifluoride is employed commercially as a dye intermediate. The treatise, Colour Index, Chemical No. 37055, Vol. 1-4, 2nd ed., 1956, Suppl. 1963, published by the Society of Dyers and Colourists (U.K.) and the American Association of Textile Chemists and Colorists (U.S.) designates this material as C.I. Azoic Diazo Component 17. It is known to couple this compound with Naphthol A.S. to produce a fade resistant red dye having the formula: ##STR1##
Colour Index, supra, indicates that 2-amino-5-chlorobenzotrifluoride is prepared commercially by the successive nitration-reduction of m-chlorobenzotrifluoride. The desired isomer is separated by freezing or other suitable means from the resulting undesired isomers and then reduced. The isomeric separation, regardless of the method employed is expensive and renders the overall process commercially unacceptable.
Whalley, J. Chem. Soc., 3016 (1949) described a process for preparing 2-amino-5-chlorobenzotrifluoride from m-aminobenzotrifluoride by acetylating to form the acetanilide derivative, then nitrating to form a 2-nitro-5-aminobenzotrifluoride, chlorinating with sodium nitrite and HCl in the presence of cuprous chloride and finally reducing the resulting nitro to an amino group. This process is a multi-step process involving at least 4 major steps.
2-Amino-5-chlorobenzotrifluoride has been prepared from N-(2-trichloromethyl-4-chlorophenyl) phthalimide by exchange fluorination with HF followed by hydrolysis as disclosed in French Patent 805,704 (1936), British Patent 459,890 (1937) and C.A., 31 4342 (1973). E. J. Forbes et al., Tetrahedron, 8 67 (1960) reports low yields by this route.
Direct chlorination of o-aminobenzotrifluoride has been attempted in assorted solvent systems in accordance with the equation: ##STR2##
The solvents utilized include water, aqueous acetic acid, aqueous hydrochloric acid and methanol. While products A and B are readily separable, the quantity of B produced varied from 14-25% of total product. Since there is no known use for this by-product, its production represents a substantial economic loss.